1. Field of the Invention
This invention relates to prevention or removal of discoloration in pyrithione, pyrithione salt and dipyrithione compositions.
2. Description of the Prior Art
The closest prior art is believed to be U.S. Pat. No. 3,890,434, issued June 17, 1975, which describes alkaline earth metal (calcium, magnesium, barium and strontium) salt adducts of dipyrithione and shampoo formulations thereof. U.S. Pat. No. 3,236,733, issued Feb. 22, 1966, describes antidandruff shampoo compositions containing pyrithione, pyrithione salts and dipyrithione. U.S. Pat. No. 3,412,033, issued Nov. 19, 1968, describes germicidal skin cleansing compositions containing pyrithione, pyrithione salts and dipyrithione.
An important problem of pyrithione, pyrithione salt and dipyrithione compositions is discoloration (usually to gray, green, blue, or purple colors). Consumer dissatisfaction and economic loss can result from such discoloration. It is believed that the discoloration results from formation of iron pyrithione from unwanted traces of iron in the compositions, which may be introduced through contaminated raw materials or contact with iron during product manufacture, handling or storage. The present invention is a solution to this problem.
3. Prior Publication
Japanese patent application disclosure No. 92881/77, published Aug. 4, 1977 (application No. 9113/76, filed Jan. 30, 1976), describes a process for preparing an aqueous suspension which comprises stabilizing zinc pyrithione in the presence of zinc oxide as a stabilizing agent. The present invention was made before Aug. 4, 1977.